1. Field of the Invention
The present invention relates to a separation type light extinction smoke detector, which can detect smoke present between a light emitting section and a light receiving section spaced therefrom, by detecting extinction or blocking of light between the light emitting section and the light receiving section, and which is particularly effective when smoke caused by a fire is to be detected.
2. Description of the Prior Art
To monitor the occurrence of a fire in an elongated space, e.g., a tunnel or pipe utility conduit, a separation type light extinction smoke detector is conventionally used. In this detector, a light emitting section and a light receiving section are separately arranged with the elongated space therebetween, and smoke present in the space is detected by detecting attenuation, due to smoke, of light from the light emitting section directed to the light receiving section. When the detector is installed, an initial condition in a normal state wherein there is no smoke is set in the light receiving section. More specifically, when the emission intensity of the light emitting section is constant, the intensity of light incident in the light receiving section varies in accordance with a distance between the light emitting and light receiving sections. When the distance between the two sections is short, a detection output at the light receiving section side is saturated and this disables detection of a change in the amount of light received caused by smoke. Therefore, the emission intensity of the light emitting section must be adjusted not to cause saturation of the detection output of the light receiving section.
To achieve the above adjustment, the characteristics of an amplifier connected to an output terminal of a light-receiving element of the light receiving section are adjusted. However, fine adjustment is required, resulting in a cumbersome operation.